Wien filter design

Abstract

A Wien filter for use in charged particle beam systems is disclosed, having two opposed resistive magnetic pole pieces separated from a set of excitation coils by an electrically insulating material. Two opposed electric pole pieces are positioned in orthogonal relationship to and in physical contact with the magnetic pole pieces to form a physical aperture through which the charged particles will pass. The resistivity of the magnetic pole pieces is such that sufficient current will flow through them between the electric pole pieces to establish a uniform electric field over the entire physical aperture.

What is claimed is: 
     
       1. A wien filter, including: two spaced-apart electric pole pieces having generally parallel opposing faces,   two spaced-apart opposed magnetic pole pieces in physical contact with said electric pole pieces such that said magnetic pole pieces and said electric pole pieces form interfaces and define a generally rectangular physical aperture, said magnetic pole pieces having a resistivity such that a current will flow through them between said electric pole pieces sufficient to establish a uniform electric field across said physical aperture,   two excitation coils, one associated with each of said magnetic pole pieces, each of said excitation coils separated from its respective magnetic pole piece by a layer of electrically insulating material.   
     
     
       2. The wien filter of claim 1, further including conductive coatings on said magnetic pole pieces at the regions of said interfaces. 
     
     
       3. The wien filter of claim 1, wherein said magnetic pole piece members have a resistivity in the range of from about 1×10 6  to 1×10 8  ohm-cm. 
     
     
       4. The wien filter of claim 1, wherein said magnetic pole piece members are made from ferrite. 
     
     
       5. The wien filter of claim 1, wherein said magnetic pole piece members are made from ferrite and said electric pole pieces are made from stainless steel. 
     
     
       6. A wien filter, including: a pair of non-magnetic, spaced-apart opposing electric pole pieces having faces in a substantially parallel relationship to one another,   a pair of spaced-apart opposing magnetic pole pieces disposed in an orthogonal relationship to said pair of electric pole pieces and sandwiching and in physical contact with said electric pole pieces to form interfaces and define a physical aperture, said magnetic pole pieces having a resistivity such that a current will flow through each one of them between said electric pole pieces sufficient to establish a uniform electric field across said physical aperture,   two excitation coils, one associated with each of said magnetic pole pieces, each of said excitation coils separated from its respective magnetic pole piece by a layer of electrically insulating material.   
     
     
       7. The wien filter of claim 6, further including conductive coatings on said magnetic pole pieces at the regions of said interfaces. 
     
     
       8. The wien filter of claim 6, wherein the resistivity of said magnetic pole pieces is in the range of from about 1×10 6  to 1×10 8  ohm-cm. 
     
     
       9. The wien filter of claim 6, wherein said magnetic pole pieces are made from ferrite. 
     
     
       10. The wien filter of claim 6, wherein said magnetic pole pieces are made from ferrite and said electric pole pieces are made from stainless steel. 
     
     
       11. A wien filter, including: a pair of non-magnetic, spaced-apart, opposing electric pole pieces having faces in a substantially parallel relationship to one another, said faces having beveled edges,   a pair of spaced-apart opposed magnetic pole pieces having faces in a substantially parallel relationship with one another, said faces having beveled edges, said magnetic pole pieces disposed in an orthogonal relationship to said pair of electric pole pieces such that the beveled edges of said electric pole pieces are in physical contact with the beveled edges of said magnetic pole piece to form interfaces and define a physical aperture, said magnetic pole pieces having a resistivity such that current will flow through each of them between said electric pole pieces sufficient to establish a uniform electric field over said physical aperture,   two excitation coils, one associated with each of said magnetic pole pieces, each of said excitation coils separated from its respective magnetic pole piece by a layer of electrically insulating material.   
     
     
       12. The wien filter of claim 11, further including conductive coatings on said magnetic pole pieces at the regions of said interfaces. 
     
     
       13. The wien filter of claim 11, wherein the resistivity of said magnetic pole pieces is in the range of from about 1×10 6  to 1×10 8  ohm-cm. 
     
     
       14. The wien filter of claim 11, wherein said magnetic pole pieces are made from ferrite. 
     
     
       15. The wien filter of claim 11, wherein said magnetic pole pieces are made from ferrite and said electric pole pieces are made from stainless steel.